1. Field of the Invention
The present invention relates generally to flight control systems, and more particularly, to a flight control system having flight control laws which enable precise aircraft maneuvering relative to the ground.
2. Description of Related Art
Aircraft which can hover and fly at low speeds include rotorcraft, such as helicopters and tilt rotors, and jump jets, like the AV-8B Harrier and F-35B Lightning II. These aircraft can spend a large portion of their mission maneuvering relative to the ground. Sometimes, this maneuvering must be conducted in confined spaces around external hazards such as buildings, trees, towers, and power lines.
For traditional flight control systems, ground-referenced maneuvering (GRM) requires the pilot to make constant control inputs in multiple axes in order to counter disturbances caused by wind, as well as to remove the natural coupled response of the aircraft. The pilot workload during such maneuvers can become quite high since the pilot must sense un-commanded aircraft motions and then put in the appropriate control input to eliminate the disturbance. In a worst-case scenario, a pilot might be required to fly GRM in a degraded visual environment. With the lack of visual cues to detect off-axis motion, the pilot might accidentally fly into an external hazard while maneuvering in a confined space.
Traditional flight control law designs do not provide the pilot with an easy way to control aircraft crab angle during GRM. Crab angle is defined as the angle between the aircraft's heading and its actual ground path. With these prior designs, adjusting crab angle while maintaining ground track took considerable pilot concentration, since the pilot had to coordinate inputs to both the lateral and directional controllers.
Although pilots generally seek to minimize crab angle during GRM, some mission tasks may call for flat yawing turns while maintaining a constant vector across the ground. For example, on a steep approach, the pilot may need to fly with a crab angle so he or she can see the landing zone. Additionally, the pilot may want to quickly transition out of rearward or sideward flight while continuing along the same ground track. In a final example, the pilot may want to acquire and track a point on the ground without having to fly directly towards it. With prior flight control designs, such maneuvers required extraordinary pilot skill to coordinate the aircraft's motions in multiple control axes.
Although the foregoing developments represent great strides in the area of flight control laws, many shortcomings remain.
While the control system of the present application is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular embodiment disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the process of the present application as defined by the appended claims.